With the vast increase in telecommunications and other communication systems over the last few decades, the use of different transmission lines using multiple conductors such as parallel conductors has increased. These communication systems include both standard copper wires and also optical fibers, which carry many more signals than the more conventional copper wire transmission systems. Much of the equipment and lines that are now in place were already in place some years ago, and include copper twisted wire pairs and optical fiber transmission lines that use digital carriers in the multiplexed scheme. When multiplexed signals are used on optical fiber, digital carrier signals are generated, and any information is digitized and forwarded over the wires on the digital carrier such as in the common T-1 and T-2 systems using pulse code modulation carriers.
In emergency repair operations or periodical maintenance and testing operations, it is necessary to sense any signals on multiple lines, such as those conductor lines that are in parallel, without disturbing communications. Some existing solutions have used break-out boxes and data acquisition techniques that involve disturbing the line or interrupting communications. These techniques have been found inadequate because it is not practical to disturb the line or interrupt communications.
Some improved devices allowed non-intrusive digital carrier signal detection, but required complicated processing circuitry. These systems did not provide information about the relative strength or identity of the digital carrier. For example, U.S. Pat. No. 5,552,702 to Buzbee, et al. discloses the system where conductive or capacitive loading can be used to detect a conductor that is in service, without disrupting service. The patent discloses a non-intrusive testing system for a digital carrier, including a balanced capacitive sensing probe coupled to a heterodyne circuit. The capacitive sensing probe is inserted between two conductor wires. The signal is obtained by capacitive or inductive coupling and is filtered to pass only the carrier signal. This signal is amplified and if the signal exceeds a threshold level, an audio tone is generated. The only information conveyed by the scheme is that the carrier signal has exceeded threshold level. The relative strength of a signal in the carrier identity is undetectable and remains unknown.
Another prior art non-intrusive testing device is disclosed in U.S. Pat. No. 5,552,702 to Wissman. This patent discloses a ferrite core used as a portion of a non-intrusive signal probe for telephone signals on a twisted wire pair. The system not only allows the detection of digital carrier signals, but also the detection of audible frequency tracing tones. A telephone repair person uses the invention to determine which wire pairs are in service by examining which wire pairs are conducting digital carrier signals. However, many of the problems associated with determining which wire is carrying signals is the cross-talk coupled signal noise. The device in the '702 patent examines which wire pairs are conducting digital carrier signals. Because the volume of an audible tone is proportional to the strength of the carrier signal, the volume of the audible tone can be used to determine if a pair is probed, in service and primarily carrying a cross-talk coupled signal. However, the system could be limited because a single probe is used to detect which lines are active. Additionally, the system is complicated and not amenable to miniaturization.
Many of these types of prior-art devices are very large, and not applicable to sensing embedded materials, or used in an application which requires sensing signals in a limited space. Additionally, the use of one sensor probe could be limited due to cross-talk existing between lines, which worsens if more parallel lines are added. Eliminating the effect of cross-talk can be essential to determine the actual presence of a signal, and is difficult if there are more than two parallel lines. Thus, the sensor sometimes must have many different elements to account for any cross-talk, especially when conductors are closely spaced, as with parallel spaced conductor lines. Thus, a sensor should have a number of different elements which would allow for more signal comparison across a parallel cable. This is especially necessary when testing on a small scale.
U.S. Pat. No. 5,315,753 to Jensen, et al. discloses an antenna structure having a number of different elements to form a patch antenna element. Although the device is not used for sensing signals, it does disclose a method of forming a structure having a plurality of antenna elements forming an antenna array. The patch antenna can be adapted for small scale use and comprises a plurality of dielectric layers, with portions of the antenna formed by a conductive paste. The device is fired to remove the binder and solidify the structure. The patch antenna conductor portion and a ground plane may be formed by silk screening the conductive paste. The antenna can be used for different types of applications including a ground positioning receiver. The patent further discloses the step of vertically stacking conductive antenna elements to permit operation at different frequencies.
It is evident that none of the prior-art devices allow a sensor that can be adapted to small scale, but also allows non-intrusive testing of conductors where the noise, such as the cross-talk, can be distinguished from the conductors carrying the regular signals.